A variety of mount assemblies are presently available to isolate vehicle vibrations, such as for automobile and truck engines and transmissions. One of the most popular mounts today is the hydraulic-elastomeric mount of the type disclosed in U.S. Pat. No. 4,588,173 to Gold et al., issued May 13, 1986 and entitled "Hydraulic-Elastomeric Mount".
The hydraulic mount assembly of this prior invention includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is partitioned by a plate into two chambers that are in fluid communication through a relatively large central orifice in the plate. The first or primary chamber is formed between the orifice plate and the body. The secondary chamber is formed between the plate and the diaphragm.
A decoupler is positioned in the orifice of the plate and reciprocates in response to the vibrations. The decoupler movement alone accomodates small volume changes in the two chambers. When, for example, the decoupler moves toward the diaphragm, the volume of the primary chamber increases and the volume of the secondary chamber decreases. In this way, at certain small vibratory amplitudes and high frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, this freely floating decoupler is a passive tuning device.
In addition to the large central orifice, an orifice track with a smaller flow passage is provided, extending around the perimeter of the orifice plate. Each end of the track has one opening; one communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the freely floating decoupler provides at least three distinct dynamic modes of operation. The operating mode is primarily determined by the flow of the fluid between the two chambers.
More specifically, small amplitude vibrating inputs, such as from smooth engine idling or the like, produce no damping due to decoupling. On the other hand, large amplitude vibrating inputs produce high velocity fluid flow through the orifice track, and accordingly a high level of damping force and smoothing action. As a third (intermediate) operational mode of the mount, medium amplitude inputs produce lower velocity fluid flow through the orifice track resulting in the desired medium level of damping. In each instance, as the decoupler moves from one seated position to the other, a relatively limited amount of fluid can bypass the orifice track by moving around the sides of the decoupler to smooth the transition between the operational modes.
Recent developments in hydraulic mount technology have led to the advent of electronic control of the dynamic characteristics of the mount. Advantageously, such a mount allows active rather than passive control of the dynamic characteristics of a mount. Thus, more efficient and effective isolation of vibrations and suppression of noises may be provided.
A previously developed hydraulic mount includes a rotary solenoid to open and close a fluid bypass port between the two fluid-filled chambers of the mount. When the bypass valve is closed, high levels of damping and rate are generated as fluid is forced from one chamber to the other through a small, fixed orifice. Conversely, when the bypass valve is open the fluid bypasses the small, fixed orifice and the mount generates very little fluid damping.
While this prior mount does provide for some control of damping characteristics in response to vehicle operating conditions, it is not without its disadvantages. More specifically, the solenoid actuator is mounted external to the mount body. Unless a high integrity seal is maintained between the mount body and the solenoid actuator, the mount fails. Due to the hostile environment of the mount, such a seal is very difficult to maintain over time. This results in the mount being susceptible to premature failure.
U.S. Pat. No. 4,583,723 to Ozawa discloses an hydraulic elastomeric mount addressing this problem. The Ozawa mount includes an electromagnetic coil mounted within the bottom plate of the mount. The movement of a two portion plate between the two chambers of the mount is controlled by the coil. This system provides either minimum damping by allowing maximum plate movement when the coil is deenergized, or maximum damping by restricting the movement when energized.
Essentially both of the prior art mounts operate in an on/off mode providing essentially either mushy or hard dynamic characteristics. Thus, effective vibration damping and noise suppression are provided by these mounts over only a relatively narrow vibration frequency range. Consequently, mounts of this type are most effectively utilized for specific applications where the vehicle component or member being damped exhibits vibrations that peak at one particular resonance frequency to which the mount is matched.
Adjustable mounts such as these, have thus proved only marginally effective in active damping situations that exist with engines and transmissions in motor vehicles. In these environments peak vibrations occur at more than one resonance frequency depending upon vehicle operating conditions. For example, an engine may vibrate at one resonance frequency during lugging, at another during rapid acceleration and at still another during sustained high RPM operation.
A need is therefore identified for an improved electronic hydraulic mount assembly that provides for selective high efficiency damping at multiple resonance frequencies exhibited by the component being damped. In this way the dynamic characteristics of the mount can be tuned, either manually or automatically, to provide the most effective and efficient damping and noise suppression of the member over the entire range of expected operating conditions.